The present invention relates to an AC-DC converter including:
an input line comprising at least two conductors, PA1 rectifying and filtering means connected to the input line, PA1 and means for monitoring and regulating a DC output voltage connected to the output of the rectifying and filtering means.
AC-DC converters generally comprise a rectifier bridge to rectify the AC current of the input line and a regulating device supplying on output of one or more regulated DC voltages. In converters without isolation between the input and output, a neutral conductor of the input line can be placed directly on the output, and will act in most cases as voltage a reference for the whole converter. Devices supplying high-power DC voltages typically include, chopper circuits, especially when the output voltage has to be greater than the input voltage. The rectifier, generally formed by diodes or thyristors, and the chopper circuits disturb the input line current increasing harmonic distortion. These disturbances are attenuated by a filtering circuit comprising inductors fitted in series on the input line before the rectifier and capacitors fitted in parallel on the rectifier output before the chopper circuits.
This filtering circuit is an LC or RLC filter of an order higher than one whose operation may be disturbed by current steps when the rectifier circuit diodes or thyristors are turned on. These current steps excite the filtering circuit and set it in oscillation at each switching. These oscillations, which are only slightly dampened by the low resistance of the circuits and of the power system, produce stray current which are superposed on the power system current. Overdimensioned filtering circuits exist which limit the oscillation effects by greatly decreasing the LC filter resonance frequency. The values of the input inductances and of the capacitors, as well as the volume and cost of the filtering circuit however, are very high.